This invention relates to a method for coating hot melt adhesives compositions to provide tack free surfaces.
Hot melt adhesives which are generally applied while in the molten or liquid state are solid at room temperature. Typically, these adhesives are provided in the form of blocks and because of the nature of these materials, particularly the pressure sensitive hot melts, there are problems associated with handling and packaging them. The solid adhesive blocks not only stick or adhere to hands or mechanical handling devices and to each other, but they also pick up dirt and other contaminants. Additionally, certain applications which require high tack formulations result in blocks that will deform or cold flow unless supported during shipment. The need and advantages for providing tackless or non-blocking hot melt adhesives are apparent and various ways of accomplishing this have been developed.
Japanese Patent 48-103635 published Dec. 26, 1973, discloses a granular adhesive which is tacky at room temperature and coated or enveloped with a non-tacky hot meltable material that is the same type or is miscible or mixable with it.
French Patent 2,544,654 published Oct. 26, 1984, discloses forming a tackless hot melt by adding molten hot melt to a mold containing a preformed support layer having a transfer film thereon which is compatible with the hot melt.
U.S. Pat. Nos. 4,748,796 issued Jun. 12, 1988, and 4,755,245 issued Jul. 5, 1988, disclose forming a protective coating for an adhesive material by electrostatically coating a mold or cavity with a powder screen and then pouring hot melt into the mold.
French Patent 2,601,616 published Oct. 22, 1988, discloses forming blocks of hot melt pressure sensitive adhesives by casting the pressure sensitive adhesive into molds precoated by spraying with a film of non self-sticking hot melt material thereby forming a fusible non-tacky veil around the pressure sensitive block.
In German Patent 22 48 046 and U.S. Pat. 4,054,632 the hot melt adhesive is squeeze-cut into pillow-shaped pieces; the pieces subsequently cooled and solidified.
European Patent 412,867 published Feb. 13, 1991, discloses a process for coating hot melt adhesives with a compatible anti-adhesive agent, the coating being done at a temperature higher than its softening point.
Still other processes involve the coextrusion of a sheath surrounding the hot-melt material where the coextruded material may be, for example, polyethylene or a non-self-adhesive "hot-melt" compatible with the formulation of the extruded product.